Possibly not related but in Minoc for instance in a bunch of the NPC houses there are specific chests labeled "A Mysterious Chest" that are always empty...?
Thats actually a pretty common key that you could acquire every time you did a Leprechaun cave when they were open. The key opened the instanced chest and was then worthless, I recall seeing dozens of them on the floor in the event center last Easter.
You can still get those keys from the spawning semi rares chests as well. The same one that spawns the tool kit. Rusty iron ones I mean.